There are many offroad camping forums where you will find current owners and a lot more information. I would be less concerned about the overall build quality than the soft side and lift mechanism reliability and the type of equipment that is used inside.
Manufacturers compete on price and there is a tendency to cut corners. I would not want a water pump or fridge to fail because the company used a less expensive version. House battery storage is also more important. My Lance hard sides has a nylon strap as a battery hold down and it would be relatively worthless for serious offroading.
The capacity of the holding tanks will be a big factor in how far afield you can go and that varies greatly between models.
A good manufacturer's website to get you started is at fourwheelcampers.com.
If I were doing serious trail running I would be getting a Toyota mini-truck with 4WD and a popup camper. I had that setup and could go anywhere my friend went with his Jeep CJ7. For more space a full size 1/2 ton is as far up as I would go as lighter trucks are going to handle the stress on trails a lot better than the heavy duty 3/4 and 1-ton trucks used by the majority of people on this forum.
